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    <title>ShellCheck: SC2021 – Don't use `[]` around ranges in `tr`, it replaces literal square brackets.</title>
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    <h1>SC2021 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC2021">See this page on GitHub</a>
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    <h2
id="dont-use--around-ranges-in-tr-it-replaces-literal-square-brackets">Don't
use <code>[]</code> around ranges in <code>tr</code>, it replaces
literal square brackets.</h2>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC2021.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="fu">tr</span> <span class="at">-cd</span> <span class="st">&#39;[a-z]&#39;</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC2021.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="fu">tr</span> <span class="at">-cd</span> <span class="st">&#39;a-z&#39;</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>Ancient System V <code>tr</code> required brackets around operands,
but modern implementations including POSIX, GNU, OS X and *BSD instead
treat them as literals.</p>
<p>Unless you want to operate on literal square brackets, don't include
them.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>If you do want to replace literal square brackets, reorder the
expression (e.g. <code>a-z[]</code> to make it clear that the brackets
are not special).</p>
<p>ShellCheck does not warn about correct usage of <code>[..]</code> in
character and equivalence classes like <code>[:lower:]</code> and
<code>[=e=]</code>.</p>
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    <p style='font-size: 80%'><a href="../index.html">ShellCheck</a> is a static analysis tool for shell scripts. This page is part of its documentation.</p>
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